This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. To date, three proteins have been identified in the fission process in yeast: Fis1, Dnm1, and Mdv1. Fis1 is targeted to the organellar membrane by a C-terminal transmembrane domain (a tail-anchored protein). Dnm1 is a large GTPase thought to act as a mechanoenzyme and belongs to the dynamin superfamily. Mdv1 is an adaptor protein. The current model we are testing is that Fis1 recruits the GTPase Dnm1 to sites of membrane scission and Mdv1 acts to further stimulate Dnm1 assembly, GTP hydrolysis, and membrane scission. We would like to complement our biochemical and NMR/x-ray structural studies with single particle reconstruction and tomography studies on this system. One goal is to build structural models of the fission machinery as a step towards understanding how these proteins couple GTP hydrolysis to membrane scission. We have obtained good expression and purification of Mdv1 constructs fused to maltose binding protein of the N-terminal domain (1-236) and the N-terminal domain with the coiled coil domain (1-302). MBP-Mdv1(1-302) appears to self-assemble, and negative stain EM reveals protofilaments that may arise from MBP, or from Mdv1 itself. This proposal is specifically to image our MBPMdv1(1-302) sample, however, we see a long-term need to work with NCMI on this project as we build up the system in the presence of membranes and other components. We seek to determine the molecular basis for mitochondrial and peroxisome fission, a process essential for organellar function and important in human health.